The present invention relates to a cam mechanism for converting rotary motion into oscillating or reciprocating motion, more particularly such a mechanism used in an animated ornamental device. The invention finds particular usage for imparting an oscillating or reciprocating movement to an ornamental object from the output of a power drive source, which may be a music box mechanism.
It is well known in the art to impart oscillating or reciprocating movement to ornamental objects, such as dolls, toys, etc., which may be supported on a housing and powered by a windup or an electric music producing mechanism. This is typically achieved by providing the power output shaft with a cam or a linkage mechanism connected to the ornamental object. Usually a tappet rod supporting the ornamental object, is journalled through the wall of a housing enclosing the mechanism and is actuated by the cam or linkage mechanism. If a cam element is used, it is typically slidably disposed within a slot provided in a follower arm, so that rotation of the cam by the output shaft imparts an oscillating movement to the tappet rod which, in turn, causes corresponding oscillation of the ornamental object.
The conventional oscillating mechanism of this type is based upon the concept of a sliding block disposed within a sliding groove and may also be known as a rocker arm, reciprocating mechanism.
While such a mechanism is relatively simple, it is inherently incapable of providing a uniform and balanced oscillating movement to the ornamental object. This is due to the geometric relationship between the cam follower arm and the associated cam which describes two arcuate paths traveled by the cam element. The beginning and the end of the paths are defined by radii extending outwardly from the cam assembly axis of rotation which intersect the cam element at two points establishing the extreme limits of the oscillation. Since the cam element must travel along a longer arcuate path during the forward half of the oscillation movement than the arcuate path required for completing the return half of the movement, it is readily apparent that each half of the oscillation motion is completed over a different time interval, and, consequently, at a different speed. The use of the known mechanism results in a non-uniform oscillation of the ornamental object.